. The Biostatistics Core (RRC-E) will serve as a resource and collaborator for the intervention studies, IS-1 and IS-2, the pilot projects, and the other RRCs. The Core leader will provide ongoing advice and recommendations regarding the statistical, sample size, and data quality implications of protocol design issues and of proposed protocol modifications. This Core will have overall responsibility for designing data entry systems, for building quality control measures into those systems, and for all data analyses. The RRC-E will: 1) collaborate with investigators on the experimental design of all projects and the design of all questionnaires and forms; 2) oversee the development and implementation of efficient and high quality data entry/management procedures for all RRCs and research projects; 3) work with investigators on an ongoing basis to ensure that the requirements of each protocol are being satisfied; and 4) oversee the statistical analysis and interpretation of all data and work with investigators in preparing publications reporting the results of the research of the OAIC. The RRC-E will also serve as a resource to new investigators in the RDC interested in gaining competence in the design and statistical analysis of intervention studies.